The nice command on Linux and Unix can be used by non-root users to set a nice value for a process that is positive or 0, but only root (or users with the proper permission) can set a nice value that is negative. Which of the following explanations is the right one?

Regular users can abuse the nice command and could assign a high priority (and more CPU time) to a process possibly in detriment to system tasks.

The nice value is an increment to the time slice for all other processes. If negative, it increases the response time for most processes on the OS, which can slow down the UI and interactive applications.

The nice field in the kernel task structure is unsigned int and cannot accept negative values.

A negative nice value gives a process extended access rights to OS resources, equivalent to a switch to kernel mode. This is dangerous if available to regular users.